The Sentinels are special forces soldiers that have had implants placed in their body. Their bones, skin, and muscles are denser and more durable, they can run faster than a humans, and have quicker reaction times and improved eyesight. Some of them have special abilities, like creating kinetic barriers that nullifies Cyclops' optic blast. Their armor (which look like the Sentinels in the comics) are even more durable than their bodies. The armor has its own oxygen supply, is covered with ceramic mind-shielding plates, and the rubber inseams prevents them from being electrocuted. They carry automatic weapons that shoot darts filled with tranqs/x-gene retardant.

Pretty much in short, they're supposed to be the government's answer to mutant powers.

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"These are the times that try men's souls... Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph."

-- Thomas Paine

"People never lie so much as after a hunt, during a war or before an election."
-- Otto von Bismarck